1. Technical Field
This invention relates to an improvement in devices for monitoring air and other gases.
More particularly, this invention relates to an improvement to the mounting means for a sampling tube used in an air or industrial gas monitoring system.
2. Description of Related Art
A common method for monitoring air and other gas streams to detect the presence of chemical agents, toxic industrial chemicals, and other compounds that might be of interest employs sorbent-packed tubes for sample collection. Those sample tubes, commonly referred to as DMMS tubes (an acronym for depot area air monitoring system) comprise a glass or stainless steel tube that is filled with a solid adsorbent such as activated carbon or a molecular sieve. The adsorbent filling is selected according to the chemicals that are being monitored.
A sample is collected by aspirating air or other sample gas through the tube for a predetermined period of time at a controlled gas flow rate. Vapors of the compounds of interest are adsorbed on the solid sorbent, and the sample tube is then removed from its sampling site for its analysis in a laboratory. The laboratory procedure commonly employed thermally desorbs the sample and passes it into an analytical system which may be, for example, gas chromatography, or gas chromatography in combination with mass spectrometry.
In field use, one end of a sample tube is connected to a vacuum manifold that maintains a known negative pressure relative to the atmosphere being sampled. If the seal between the sample tube and the manifold is not secure and leakage occurs, then the sample results are compromised and cannot be trusted. Forming a secure seal on the end of a sample tube is difficult because an end seal requires that the tube end meet strict requirements for flatness and squareness. A chip or other imperfection on the tube end creates a potential leakage site causing an end seal to fail. It is also possible to use an O-ring to form a seal on the outside diameter of the tube, but that type of seal often makes it difficult to insert the tube end into and to remove it from a mating fitting on the vacuum manifold. That is particularly true if the tube is enclosed in some manner in order to protect it from physical damage. Another complication arises from the fact that variation in the length of sample tubes is common.
The device disclosed and claimed in this application overcomes all of those problems, and does so in a simple, dependable, and cost effective manner.